fn main (){
    let a=Some(2);
    if let Some(x) = a {
        println!("print the a's value {}", x);
    }else{
        ()
    }

    //println!("the value x's life scope {}",x);
    let b = Some(1999);
    let v = if let Some(y) = b {
        y
    }else{
        0
    };
    println!("the b's value is {}", v);
}
